Hydroxylammonium salts may be represented by the formula: EQU (NR.sub.2 HOH).sup.+.sub.y X.sup.-y
wherein each R is hydrogen or a hydrocarbon group containing from 1 to about 8 carbon atoms, X is an anion of an acid and y is a number equal to the valence of X. Hydroxylammonium salts are compounds which have a variety of applications. For instance, hydroxylammonium nitrate may be used as a component of liquid propellant and as a reducing agent in photographic graphic operations. In some of these applications, it is desirable that a hydroxylammonium salt solution of high purity is available.
There exist several production methods to manufacture hydroxylammonium salts. In the case of hydroxylammonium nitrate for example, some of these methods include: electrodialysis of hydroxylammonium chloride and nitrate; reaction of hydroxylammonium sulfate and barium nitrate; three-step cation exchange process employing hydroxylammonium sulfate and nitric acid; and electrolytic reduction of nitric acid. Some of these methods, however, do not provide hydroxylammonium salt solutions of high purity which some applications of the compound require. As a result, procedures have been developed to purify the hydroxylammonium salt solutions produced by existing methods. Nevertheless, there remains a substantial demand for large quantities of high purity hydroxylammonium salt solutions.
Hydroxylamine is useful as an intermediary in chemical processes especially in the pharmaceutical and agricultural industries. It is also useful in stripper formulations. Stripper formulations may be used to remove photoresists from or clean a substrate. For example, hydroxylamine stripper solutions are used to remove polyamide coatings from metal foil. Hydroxylamine stripper solutions are utilized in the printed circuit board and semiconductor industries.
Frequently, solutions of hydroxylamine, especially solutions prepared from hydroxylammonium salts, contain undesirable amounts of impurities such as salts, ammonium ions, metals and organic materials. Thus, there also exists a need for hydroxylamine solutions having high purity.
French Patent 2,602,802 is directed to an electrolytic process to directly produce high purity solutions of hydroxylammonium nitrate from nitric acid. In particular, a process is described for producing by electrolysis a hydroxylammonium nitrate solution in an electrochemical cell containing a cathode compartment, an anode compartment and a separator between the cathode compartment and anode compartment. The process is characterized in that it includes the following operations: (a) introducing a catholyte, essentially containing an aqueous nitric acid solution, in the cathode compartment; (b) introducing an anolyte solution into the anode compartment; (c) electrolyzing the catholyte to a cathode potential between about 0.5 and 1.4 volts compared to the standard calomel electrode, while keeping the temperature of the reaction to the cathode below about 50.degree. C., in order to produce a hydroxylamine solution; and (d) recovering the hydroxylammonium nitrate solution from the cathode compartment.
U.S. Pat. No. 4,645,579 relates to aqueous solutions of hydroxylamine which are prepared from aqueous hydroxylammonium salt solutions by electrodialysis by a method in which the aqueous hydroxylammonium salt solution is fed into the middle zone of an electrolysis cell, which is divided into a cathode zone, an anode zone and a middle zone by means of semipermeable membranes, and is electrolyzed, and the catholyte used is an alkali metal hydroxide solution containing ammonia and/or amines.
The production of hydroxylamine by the electroreduction of nitric oxide in sulfuric acid is described by L. J. J. Janssen et al in Electrochimica Acta, 1977, Vol. 22, pp. 27-30 and by M. L. Bathia et al in The Canadian Journal of Chemical Engineering, Vol. 57, October 1979, pp. 631-7. Janssen et al utilize a platinum cathode, and Bathia et al utilize a cathode bed of tungsten carbide particles. The electroreduction of nitric oxide on bulk platinum in perchloric acid and sulfuric acid solutions is described by J. A. Colucci et al in Electrochimica Acta, Vol. 30, No. 4, pp. 521-528, 1985.
U.S. Pat. No. 5,281,311 relates to a process in an electrolysis cell involving (A) providing an electrolysis cell containing an anolyte compartment containing an anode, a catholyte compartment containing an oxygen-consuming cathode and an anionic divider separating the anolyte and catholyte compartments; (B) providing an aqueous solution containing an acid and water to the anolyte compartment, and an aqueous solution containing hydroxylamine salt, water and optionally, an acid to the catholyte compartment; (C) charging an oxygen-containing gas to the catholyte compartment; (D) passing a direct current through the electrolysis cell for a period of time effective to reduce the acid content in the catholyte compartment and/or to convert the salt to a hydroxylamine; and (E) recovering a hydroxylamine or a hydroxylamine salt solution containing a reduced amount of acid from the catholyte compartment.
U.S. Pat. No. 5,447,610 relates to preparing hydroxylamine and hydroxylammonium salts by electrolytically reducing a mixture containing at least one nitrogen oxide and either a neutral electrolyte to form hydroxylamine or an acidic electrolyte such as an organic or inorganic acid to form a hydroxylammonium salt. The electrolytic reduction is conducted in an electrolysis cell containing an anolyte compartment containing an anode, a catholyte compartment containing a cathode, and a divider separating the anolyte and catholyte compartments where the mixture of at least one nitrogen oxide and the electrolyte is present in the catholyte compartment, and an acid is present in the anolyte compartment.